Soru

A $42$-year-old woman is evaluated in the clinic due to progressive fatigue, constant chilling, and a $6$-kg ($13.2$-lb) weight gain over the past $6$ months. She also reports worsening shortness of breath when climbing stairs, frequent morning headaches, and a tendency to bump into objects on her sides. She has not had a menstrual period in $8$ months. Her medical history is unremarkable, and she takes no medications. Vital signs show a temperature of $36.1^\circ$ C ($97.0^\circ$ F), blood pressure of $88/58$ mmHg, pulse of $54$/min, and respiratory rate of $14$/min. Physical examination reveals a lethargic, pale woman with a delayed relaxation phase of the deep tendon reflexes. Visual field testing reveals bitemporal hemianopsia. She has non-pitting edema of the bilateral lower extremities. The lungs are clear to auscultation.

Laboratory studies reveal:
Sodium: $131$ mEq/L
Potassium: $4.1$ mEq/L
Creatinine: $0.8$ mg/dL
Thyroid-stimulating hormone (TSH): $1.1$ $\mu$ U/mL (Normal: $0.4$–$4.0$ $\mu$ U/mL)
Free thyroxine (T4): $0.4$ ng/dL (Normal: $0.9$–$2.4$ ng/dL)

Which of the following is the most appropriate next step in management?